If you walked into a room and found that it was too hot, would you, as a first step:

Measure the air to find anomalies in the mix of gasses

Count the number of people in the room, to assess the effect of body heat on the room’s temperature

Check the thermostat on the furnace

If you answered #3, sorry, but you can’t join the IPCC. If you really want to irritate an AGW supporter, ask about the sun. To AGW supporters, only a Luddite would check the sun’s output when they could instead be obsessing over the increase in CO2 by 0.009% of the atmosphere.

When they looked at the problem, the IPCC decided that over the last 50 years, the sun has been irrelevant to warming. Note that the blue band in this chart (described in more detail in the last section), the IPCC thinks that without man, the world would have cooled over the last 50 years:

Further, when they detailed different climate forcings, the forcing from changing solar irradiance was a trivial rounding error (though they had the good grace to mark their understanding of this as “low”) meaning the sun has very little effect vs. what the sun had in 1850 (in the Little Ice Age!)

But it turns out, interestingly, that solar irradiance may be close to its highest point in centuries. Al Gore says that current global temperatures are the highest they have been in 1000 years. A new study by the Institute of Astronomy in Zurich says that the "sun is more active now than it has been at anytime in the previous 1,000 years." Related?

Sunspots have been monitored on the Sun since 1610, shortly after the invention of the telescope. They provide the longest-running direct measurement of our star’s activity.

The variation in sunspot numbers has revealed the Sun’s 11-year cycle of activity as well as other, longer-term changes.

In particular, it has been noted that between about 1645 and 1715, few sunspots were seen on the Sun’s surface.

This period is called the Maunder Minimum after the English astronomer who studied it.

It coincided with a spell of prolonged cold weather often referred to as the "Little Ice Age". Solar scientists strongly suspect there is a link between the two events – but the exact mechanism remains elusive….

But the most striking feature, he says, is that looking at the past 1,150 years the Sun has never been as active as it has been during the past 60 years.

Over the past few hundred years, there has been a steady increase in the numbers of sunspots, a trend that has accelerated in the past century, just at the time when the Earth has been getting warmer.

The data suggests that changing solar activity is influencing in some way the global climate causing the world to get warmer.

We can look at solar output over large time frames by looking at the production of carbon-14 (less is produced in years of high solar activity, and vice versa). The analysis below used the ratio of oxygen isotopes in the stalagmites to estimate the water temperature at the time they were formed. The result is an interesting correlation between solar activity and a global temperature proxy over a long time-scale (Graph from Neff et al., 2001):

Over the last 1000 years, we see that (again using a reversed scale of C14 as a proxy) solar activity is highly correlated with long term temperature trends (I have used the pre-Mann chart, because while it may over-emphasize the Medieval Warm Period, I still think such a period existed).

Solar Output Anomaly

Temperature Anomaly

Look at the following reconstruction data by Judith Lean of the Naval Research Library and charted from her data at NOAA by Junkscience.com shows that interestingly, the sun’s output does appear to be higher today than they have been in many, perhaps hundreds of years

Would such increased activity be expected to result in higher Earth temperatures? I don’t know, and there are some issues one has to be careful with on this chart. Most importantly the scaling: While the shape of the curve looks a lot like the temperature trend over the last 400 years, note that the entire variation from the low to the high point is only about 0.25% – the scaling makes it look more dramatic. Of course, the same could be said for global temperature, where a half degree C temperature increase on an absolute Kelvin scale would only be about 0.17%, so an argument can be made that on a percentage basis, this change in irradiance is about the same order of magnitude as our change in temperature. A more sophisticated comparison might say that since black body radiation is related to absolute temperature to the fourth power, .25% increase in irradiance would be expected to heat the Earth by .06%.

The chart on the above left compares the recent temperature anomaly to solar irradiance, while the chart on the right compares it to CO2 concentrations. Neither is a beautiful fit (and one may have to include aerosols in either scenario to account for 1970’s cooling) but solar irradiance seems at least as good as that of CO2. Remember, the IPCC shows the world cooling due to solar effects during the same time the red solar irradiance line is peaking.

Recently Alexander et. al. in have done some very comprehensive work relating solar irradiance and rainfall. The study posits that one of the reasons for less than perfect fit of sunspot and irradiance data with temperature is that the Sun actually works on a 21 year cycle when the sunspot cycle is combined with the cyclical wobble of the Suns motion through space. The study concluded:

The Intergovernmental Panel on Climate Change (IPCC) (2001) dismisses the view that solar activity has a meaningful influence on global climate. The basis for this view is that variations in the receipt of solar activity are too small to account for variations in the climatic responses. These variations were determined from satellite and other observations. What the IPCC scientists failed to appreciate is that changes in the level of solar radiation received on earth are amenable to precise calculation. The variations are well in excess of the IPCC value of +0,3 Wm–2 quoted earlier.

One of the interesting things about solar output is that, if it is really higher, we should see effects on other planets, not just on Earth. And, in fact, a lot of evidence has been pouring in over the last 5 years from astronomers (not climate guys) that the rest of the solar system has been warming dramatically.

Take Mars, for example. Mar’s ice caps have been melting and diminishing since NASA’s Mars Global Surveyor and Odyssey started to measure them around 2002.

Changes in the red spot on Jupiter seem to be a sign of warming temperatures. And Neptunes moon Triton is warming. We have to be careful with how we draw conclusions on these outer planets, since their “year” is so long, seasonal changes can last decades.

As seen in Figure 1, Neptune has been getting brighter since around 1980; furthermore, infrared measurements of the planet since 1980 show that the planet has been warming steadily from 1980 to 2004. As they say on Neptune, global warming has become an inconvenient truth. But with no one to blame, Hammel and Lockwood explored how variations in the output of the Sun might control variations in the brightness of Neptune.

Figure 1 (a) represents the corrected visible light from Neptune from 1950 to 2006; (b) shows the temperature anomalies of the Earth; (c) shows the total solar irradiance as a percent variation by year; (d) shows the ultraviolet emission from the Sun (Source: Hammel and Lockwood (2007)).

What would seem so simple statistically is complicated by the degrees of freedom in the various time series which is related to the serial correlation in the data (e.g., next year’s value is highly dependent on this year’s value). Nonetheless, they find that the correlation coefficient between solar irradiance and Neptune’s brightness is near 0.90 (1.00 is perfect). The same relationship is found between the Earth’s temperature anomalies and the solar output. Hammel and Lockwood note “In other words, the Earth temperature values are as well correlated with solar irradiance (r = 0.89) as they are with Neptune’s blue brightness (|r| > 0.90), assuming a 10-year lag of the Neptune values.” The temporal lag is needed to account for the large mass of Neptune that would require years to adjust to any changes in solar output.

Hammel and Lockwood conclude that “In summary, if Neptune’s atmosphere is indeed responding to some variation in solar activity in a manner similar to that of the Earth albeit with a temporal lag” then “Neptune may provide an independent (and extraterrestrial) locale for studies of solar effects on planetary atmospheres.”

One of the problems with irradiance as a driver for climate change is that though the changes seem to be fairly well correlated with the temperature anomaly, many scientists think the magnitude is too small to totally account for temperature changes. It is ironic that AGW supporters use this as a refutation of the sun’s effect, since they have exactly the same problem with CO2, and must posit huge positive feedback loops to justify their forecasts.

A second, newer theory has emerged as to a potential second warming effect of solar output. To understand it, we have to start with clouds. For those that don’t live in a hot climate like I do here in Phoenix, I will give everyone a bit of background – clouds cool things off. Ok, as with everything in climate, things are actually far more complicated – high clouds can sometimes cause warming, and nighttime clouds can actually slow cooling. Never-the-less, in general, cloudcover cools things off by blocking out and reflecting the sun’s energy.

Clouds are in fact such a strong cooling force that is has been estimated by several sources (Theodor Landscheidt, 1998) that having clouds cover 1% more of the Earth’s surface would cancel the heating effect of a doubling of CO2. In fact, it was one of my criticisms earlier that AGW theory seems overly intent on finding positive feedback loops, while not considering negative feedbacks seriously enough – one such potential negative feedback is that on a warmer Earth, more water is evaporated into clouds, in turn cooling things back off.

But recently, an interesting new theory on cloud formation has emerged. In short, it holds that cosmic rays, which are the high energy particles that arrive at Earth from supernovas, spur cloud formation by ionizing air molecules that act as seeds for water condensation and cloud formation. This sounds wild, but really no wilder than warming by a gas (CO2) that makes up a near trivial portion of the atmosphere. Like CO2 warming, this effect has been observed in various laboratory chambers. But is it really a measurable driver of climate?

So what changes cosmic ray flux to the Earth? The biggest influence is the sun. When the sun’s output is high, cosmic rays are prevented from hitting the Earth, and vice versa. So high solar activity corresponds to low cosmic ray flux and therefore lower cloud formation and higher temperatures.

While the link between solar irradiance levels and warming is pretty straight forward, the cosmic ray cloud formation proposition is still in its infancy. Those of us who criticize AGW supporters for running past the evidence on CO2 should not make the same mistake on cosmic rays, and movies such as The Global Warming Swindle have gone too far in portraying this alternate theory as fact.

Recently, Roger Pielke has done a substantial amount of research on a different type of anthropogenic forcing. Specifically, he has hypothesized that man’s changing patterns of land use can be a substantial driver of regional climate, including temperature and even more particularly, precipitation. For example, clearing relatively dry land and replacing it with irrigated agriculture substantially changes to the local heat balance, not the least by increasing humidity. Dr. Pielke explains summarizes the consequences on his web site:

Humans are significantly altering the global climate, but in a variety of diverse ways beyond the radiative effect of carbon dioxide. The IPCC assessments have been too conservative in recognizing the importance of these human climate forcings as they alter regional and global climate. These assessments have also not communicated the inability of the models to accurately forecast the spread of possibilities of future climate. The forecasts, therefore, do not provide any skill in quantifying the impact of different mitigation strategies on the actual climate responsethat would occur.

There is no area in global warming discussions where AGW advocates have done more to shoot down their own credibility than in the absolutely egregious science and absurd claims that have been made about the potential negative effects of global warming. If AGW advocates are frustrated that skeptics question their science and their credibility, they need to look no further than their own claims on global warming effects, which are so easy to prove wrong that it causes people like me to question everything else they say.

Whenever global warming is discussed in the press, the consequences are all universally bad. Floods, famine, drought, pestilence, disease – they are all commonly predicted results of global warming. But it is worth noting that in the 1970’s, when climate scientists and the press were in a panic over global cooling, the predicted results were… floods, famine, drought, pestilence, disease. The implication is that we currently happen to be balanced on the knife edge of exactly the optimum world temperature for mankind. Any change warmer or cooler results in net negative consequences.

This, of course, seems an odd coincidence. Since man evolved into homo sapiens, he has experienced a wide range of cooler and warmer temperatures than we experience today. It seems frankly amazing that in the mid 20th century we happened to be sitting at the absolute ideal temperature for modern technological society and agriculture. Now, I guess you can argue that our society has made enormous investments based on the locations of the best crop lands, the height of the oceans, the typical paths of storms, etc., and that shifts in any of these would force an expensive restructuring of these investments. However, it is also worth noting that from the bottom of the Little Ice Age to say 1980, the world warmed at least a degree, and no one really noticed! Everyone was still talking about cooling!

So I think that any honest analysis of the effects of global warming would have to acknowledge that there are likely both positive and negative effects. While some areas may experience heat-induced droughts, other will be wetter as more moisture from the oceans is evaporated. While some crops will struggle, others, particularly in northern latitudes, will thrive due to longer growing seasons. For each crop of vegetables that wilt in a heat wave there will be a crop of citrus that didn’t freeze. While more may die from the heat, fewer will die from the cold. These may still net to a negative sum, but that net sum will be substantially less negative than a one-sided look at only the downsides of warming would arrive at.

One reason that warming impact analysis is hard is because while we may talk about the world warming a degree or two, the world does not warm evenly. Most climate models show the most warming on dry winter nights (Siberian winters, for example, get a disproportionate share of the warming). An extra summer degree in Arizona would suck; an extra winter degree in Siberia would probably be welcomed, and would likely extend growing seasons.

In the rest of this chapter, I will spend some time with a number of the most common “scary results” from global warming.

In An Inconvenient Truth, Al Gore claims that oceans will rise twenty feet due to global warming. Helpfully, a number of websites have been created to show what parts of the world (including much of Florida) would sink beneath the oceans like Atlantis with a 20-foot rise in sea level.

Fortunately, even most AGW supporters believe that Gore is wildly exaggerating, at least for any time period less than a couple of centuries. The Fourth IPCC report (see chart below) predicts sea level rise by the year 2100 of … 12-15 inches. And remember that this is based on forecasts of both CO2 production and climate sensitivity to CO2 that are arguably high by a factor of two or more. From the fourth IPCC report (different columns are for different starting CO2 forecasts):

By the way, to give a sense of scale, the IPCC estimates that the oceans have already risen about 0.2 meters in the last 130 years or so:

One other interesting thing you can see from the sea level forecast chart is that even the IPCC considers ice melting virtually irrelevant. That is because most of the surface level increase is from thermal expansion of the water as the oceans warm. In the A1B case, for example, net worldwide ice melt raises oceans by about 4 inches in the next hundred years.

This last conclusion may seem crazy to anyone who has watched the media of late or seen Mr. Gore’s movie. Images of ice crashing into the ocean and sea ice retreating are common fodder for global warming visuals. But the fact is that ice, like everything else in climate, is complicated.

North Pole: Arctic sea ice melting is totally irrelevant to ocean surface levels. Since the ice floats, even a 100% melting of the Arctic ice will not change sea level one bit, just as ice melting in your glass of water does not cause your glass to overflow.

But some may argue that this ducks the question. Does current, well-documented retreat of artic ice sheets provide independent confirmation of the magnitude of AGW? In fact, though ice sheets are retreating, this seems to be part of a two hundred year trend that began long before man was burning fossil fuels in any quantity:

Alpine Glaciers: We know that many Alpine glaciers around the world are retreating. Some of this is surely from global warming, but some is also from fluctuations in precipitation. In many cases, we have documented evidence that these glaciers have been retreating since the 19th century, and that they have been less extensive in the past.

Reid A. Bryson is Emeritus Professor and founding chairman of the University of Wisconsin Department of Meteorology—now the Department of Oceanic and Atmospheric Sciences and a member of the United Nations Global 500 Roll of Honor. When asked about the retreat of Alpine glaciers, he says, “What do they find when the ice sheets retreat, in the Alps? A silver mine! The guys had stacked up their tools because they were going to be back the next spring to mine more silver, only the snow never went,” he says. “There used to be less ice than now. It’s just getting back to normal.”

Alaska Geographic published a chart of the retreat of the glaciers at Glacier Bay, Alaska, showing most of the retreat occurred before the 2nd half of the 20th century:

One special note should be made of the glaciers on Kilimanjaro, because their retreat over the last 125 years has been well-documented and played a starring role in An Inconvenient Truth. Analysis has shown that most the glacial retreat at Kilimanjaro occurred before 1953 (and therefore before most recent warming) and that the retreat has more to do with moisture in the air than with global warming. One wonders why the movie, with glacial retreats around the world that are provably due to warming, would focus on one that is probably not due to warming.

·Greenland: Greenland has a lot of ice, and there is not much doubt that if it all melted, the oceans would rise a lot. However, we know that in the middle ages, Greenland was much warmer and had less extensive ice coverage (thus the name Greenland and the successful attempt to farm it for over a century)

While there is a lot of discussion about whether the Medieval Warm Period extended worldwide, most accept that it did cover the North Atlantic, including Greenland. Boreholes, such as the Dahl-Jensen below, seem to prove out our historical information, showing a temperature peak around the year 1000.

·Antarctica: Something like 80-85% of the world’s ice is in Antarctica. And no one really thinks it is melting or going to melt. In fact, if you look at the marks on the IPCC chart above for the contribution of Antarctic ice to ocean levels, it has a net negative impact, which means the IPCC actually expects the Antarctic ice sheet to grow, not melt.

Whoa, that can’t be right! Mr. Gore showed those videos of ice retreating in Antarctica. Well, yes, sort of. Scientists expect that global warming will make the sea currents that circle Antarctica a bit warmer, leading to more precipitation and more snowfall on the continent. Besides, Antarctica is so damn cold that raising temperatures a few degrees is not going to melt anything.

The one exception is the Antarctic Peninsula, which sticks out into the warmer oceans. This land area, representing about 2% of the Antarctic land mass and even less of its total ice sheet, is expected to warm and lose ice while the other 98% gains ice.

Guess what? Mr. Gore chose that little 2% to illustrate his movie. Was he ignorant of the choice he was making, or did he know exactly what he was doing, telling the literal truth (that the peninsula is melting) but leading viewers to the wrong conclusion overall about Antarctic ice?

By the way, one last interesting fact that frankly, scientists don’t fully understand is the fact that the South Pole is really not experiencing any warming. While the warming at the north pole exceeds the global average, the south pole shows little or no anomaly.

Alter Hurricane Katrina, the media storyline focused strongly on the role global warming may have played in increasing hurricane power and activity. Lost in the rush to blame global warming was the fact that Katrina, when it made landfall, was not even a category 5 hurricane, and its devastation was due more to a city sited below sea-level that did a poor job of managing its storm protection.

In fact, many hurricane experts do not agree with the argument that warming oceans can lead to more and stronger hurricanes. In fact, hurricane activity is more related to the difference in temperatures between the cold and warmer waters, a difference AGW theory says should decrease rather than increase. So is there reason to believe hurricanes are on the rise as global temperatures warm? The answer, as shown below, seems to be no:

But what about storm damage? It certainly seems like recent hurricanes have resulted in far more economic damage. And they have, but for the simple reason that over the last several decades, Americans have put billions of dollars of expensive homes and other facilities in vulnerable Gulf and Atlantic coast locations. Several years ago, Dr. RA Pielke and CW Landsea (that can’t really be the name of a scientist studying coastal strikes by hurricanes) attempted to correct hurricane damage numbers for the density and value of coastal real estate:

By this reckoning, it is hard to see any trend.

Another claim Mr. Gore makes in An Inconvenient Truth is that 2004 was the most active year for tornadoes ever in the United States, and that there has been a steady trend in increasing tornados as the globe has warmed.

And certainly if you look at the raw numbers, you might be worried:

But there is a little something Mr. Gore fails to mention. During this time period, from 1950 to 2000, the technology and network for detecting tornados has improved vastly. From the NOAA

With increased national doppler radar coverage, increasing population, and greater attention to tornado reporting, there has been an increase in the number of tornado reports over the past several decades. This can create a misleading appearance of an increasing trend in tornado frequency. To better understand the true variability and trend in tornado frequency in the US, the total number of strong to violent tornadoes (F3 to F5 category on the Fujita scale) can be analyzed. These are the tornadoes that would have likely been reported even during the decades before Dopplar radar use became widespread and practices resulted in increasing tornado reports. The bar chart below indicates there has been little trend in the strongest tornadoes over the past 55 years.

Oops! In fact, tornado frequency seems to be falling as temperatures warm. Do you think this was another honest mistake, like with Antarctica, or did Mr. Gore purposefully obfuscate the real story?

Another argument is that global warming will lead to more temperature extremes, particularly record sweltering highs. That seems logical enough, but Bruce Hall actually compiled the data and found something interesting. He created a data base for each state which shows in what year that state’s monthly temperature records were set. So for each state, he has the years when the twelve monthly high temperature records were set (e.g. year of highest Arizona Jan temp, year of highest Arizona Feb temp, etc.) and the years when the twelve monthly low temperature records were set. Here, for example, is his data for Arizona:

So, for example, the record for the highest July temperature was set in 1905 at Parker, Arizona with a scorching 127 degrees. The entry in his database would then be Arizona-July: 1905. He notes that there is a bias in the data toward more recent years, since if the record was set in 1905 and tied in 1983, only the newer 1983 date will show in the data. I would also observe that this data is uncorrected for urban heat island effects (as cities urbanize they get hotter, and effect that is different than CO2-cause global warming and is usually corrected for in global warming studies). There is also a bias towards the present in having more measurement points today than 100 years ago: More measurement points means that, over a state, one is more likely to pick up the true high (or low).

Though I have other problems with the anthropogenic global warming hypothesis, I have never really doubted that the world has warmed up over the last century. So even I, a skeptic, would expect a disproportionate number of the all-time high temperatures to be in the last decade, particularly without UHI correction and with the bias discussed above. The global warming folks would argue that the effect should be doubly pronounced, since they claim that we are seeing not just a general heating, but an increase in volatility (ie more extreme variation around the mean).

But Hall doesn’t find this when he graphs the data. Take the 600 state monthly high temperature records that exist on the books today (50 states times 12 months) and graph the distribution of years in which these records were set:

Assuming about 120 years of data, you should expect to see a high temperature record on average in a database of 600 records at 5 per year, which is precisely where we have been of late and well below the record years in the thirties (remember the dust bowl?) and the fifties. It seems to actually show a reduction in temperatures or volatility or both.

This may seem impossible – how can the mean increase without causing a lot more new highs? But remember what we discussed earlier – global warming is expected to be seen disproportionately in nighttime and winter temperatures. This means that the mean can increase even as daytime summer highs don’t increase much. In a sense, is the lows, not the highs, that are getting higher.

Vincent et al in 2005 did a study of temperature trends in South America from 1960-2000. What they observed is exactly what we discussed here: The number of warm days and cold days did not really change. The warming trend showed up as a decrease in cold nights and an increase in warm nights, meaning effectively that the diurnal (across 24 hours) temperature variation is narrowed.

Biologist Josef Reichholf was interviewed recently in der Spiegel. He is a strong conservationist, and certainly has his axe to grind with industrial society. In fact he blames industrial agriculture and modern development for problems that species face.

Many species are certainly threatened, but not by climate change….Many species have already fled from the countryside to the cities, which have been transformed into havens of biodiversity. We are also seeing another interesting phenomenon: Major cities, like Hamburg, Berlin and Munich, have formed heat islands where the climate has been two or three degrees warmer than in the surrounding countryside for decades. If higher temperatures are truly so bad, why do more and more animals and plants feel so comfortable in our cities?

On the contrary, there is much to be said for the argument that warming temperatures promote biodiversity. There is a clear relationship between biodiversity and temperature. The number of species increases exponentially from the regions near the poles across the moderate latitudes and to the equator. To put it succinctly, the warmer a region is, the more diverse are its species.

OK, but what about those polar bears? We have all seen the media pictures of bears stranded on blocks of ice, as if all the arctic has melted out from under them. Well, it turns out that polar bears have survived much warmer conditions. We know polar bears existed as a separate species at least 125,000 years ago, and in the intervening years, there have been periods where Arctic sea ice melted completely during the summer months. And yet polar bears still exist today. Polar bears may be threatened by man’s hunting and encroachment on its hunting grounds, but not likely by our fossil fuel combustion.

AGW fear-mongering also extends to breathless predictions of increases in “tropical” diseases. Reichholf also takes on this canard:

Many people truly believe that malaria will spread as temperatures rise. But malaria isn’t even a true tropical disease. In the 19th century, thousands of people in Europe, including Germany, the Netherlands and even Scandinavia, died of malaria, even though they had never gone abroad. That’s because this disease was still prevalent in northern and central Europe in previous centuries. We only managed to eliminate malaria in Europe by quarantining the sick, improving hygiene and draining swamps. That’s why I consider it virtually impossible that malaria would return to us purely because of climate change. If it does appear, it’ll be because it has been brought in somewhere.

Most of the world’s leading tropical disease experts tend to agree with Reichholf. In fact, I would argue that diseases like Malaria are not diseases of the tropics but diseases of poverty and under-development. Malaria is prevalent in Africa not because Africa is hot but because Africa is poor. Asian tropical countries that have developed substantially over the last several decades have also greatly reduced malaria. In fact, as I will discuss in later sections, by reducing world economic growth and slowing development in the third world in the name of CO2 reduction, we will actually increase rather than reduce these diseases.

One of the recent hysteria’s has been that global warming will cause the Gulf Stream to collapse as Atlantic circulation patterns are radically altered, thus leading to the freezing of Europe. More sober scientists have since essentially said “nevermind.” The Gulf Stream and Atlantic circulation patterns are far more robust than this theory assumed, and, even if the Gulf Stream changes, proponents of the theory were overestimating the dependence of Europe on Gulf Stream warming.

Interestingly, we may eventually decide that other non-climate effects of CO2 production actually present more tangible environmental threats. In particular, recent studies have shown that more atmospheric CO2 is causing the PH of ocean surface layers to drop (ie become more acidic) leading potentially to coral kills and substantial changes in sea life. At the same time, physicist Freeman Dyson argues that stratospheric cooling from man-made CO2 is much more a problem than surface warming, and is much more measurable and provable. These topics are beyond my scope at this point, but something we may see more of in the future.

Kyoto Treaty

In the mid-1990’s, a number of western nations crafted a CO2-reduction treated named Kyoto for the city in which the key conference was held. The treaty called for signatory nations to roll back their CO2 emissions to below 1990 levels by a target date of 2012. Japan, Russia, and many European nations signed the treaty; the United States did not. In fact, the pact was ratified by 141 nations, but only calls for CO2 limits in 35 of these (so the other 106 were really going out on a limb signing it). China, India, Brazil and most of the third world are exempt from its limits.

We will discuss the costs and benefits of CO2 reduction a bit later. However, it is instructive to look at why Kyoto was crafted the way it was, and why the United States refused to sign, even when Al Gore was vice-president.

The most obvious flaw is that the entire developing world, including China, SE Asia, and India, are exempt. These countries account for 80% of the world’s population and the great majority of growth in CO2 emissions over the next few decades, and they are not even included. If you doubt this at all, just look at what the economic recovery in China over the past months has done to oil prices. China’s growth in hydrocarbon consumption will skyrocket over the coming years, and China is predicted to have higher CO2 production than the United States by 2009.

The second major flaw with the treaty is that European nations cleverly crafted the treaty so that the targets were relatively easy for them to make, and very difficult for the United States to meet. Rather than freezing emissions at current levels at the time of the treaty, or limiting carbon emission growth rates, the treaty called for emissions to be rolled back to below 1990 levels. Why 1990? Well, a couple of important things have happened since 1990, including:

a.European (and Japanese) economic growth has stagnated since 1990, while the US economy has grown like crazy. By setting the target date back to 1990, rather than just starting from day the treaty was signed, the treaty effectively called for a roll-back of economic growth in the US that other major world economies did not enjoy.

b.In 1990, Germany was reunified, and Germany inherited a whole country full of polluting inefficient factories from the old Soviet days. Most of the dirty and inefficient Soviet-era factories have been closed since 1990, giving Germany an instant one-time leg up in meeting the treaty targets, but only if the date was set back to 1990, rather than starting at the time of treaty signing.

c.Since 1990, the British have had a similar effect from the closing of a number of old dirty Midlands coal mines and switching fuels from very dirty coal burned inefficiently to more modern gas and oil furnaces and nuclear power.

d.Since 1990, the Russians have an even greater such effect, given low economic growth and the closure of thousands of atrociously inefficient communist-era industries.

It is flabbergasting that US representatives could allow the US to get so thoroughly out-manuevered in these negotiations. Does anyone in the US really want to roll back the economic gains of the nineties, while giving the rest of the world a free pass? Anyway, as a result of these flaws, and again having little to do with the global warming argument itself, the Senate voted 95-0 in 1997 not to sign or ratify the treaty unless these flaws (which still exist in the treaty) were fixed. Then-Vice-President Al Gore agreed that the treaty should not be signed without modifications, which were never made and which Europeans were never going to make.

By the way, enough time has elapsed that we have data on the progress of various countries in meeting these targets. And if you leave out various accounting games with offsets of dubious value, most all the European nations, despite all the advantages described above, are still missing their targets. The political will simply does not exist to hamstring their economies to the extent necessary to roll back CO2 growth. Actual growth rates for CO2 emissions have been (source UN):

United States

Europea Union

1990-1995

6.4%

-2.2%

1996-2000

10.1%

2.2%

2001-2004

2.1%

4.5%

You can see that the Europeans positioned themselves well in the 1990’s to make their targets. Realize that as the treaty was negotiated, they already had a good idea of these numbers for 1990-1995 and even a few years beyond. They knew that by selecting a 1990 baseline, they were already on target to meet the goals and the US would be far behind. Again, realize that the 1990-2000 EU performance on CO2 production had nothing to do with post-Kyoto regulatory responses and everything to do with the economic fundamentals we outlined above that would have existed with or without the treaty.

Since 2000, however, it has been a different story. European emissions have increased as their economies have recovered, at the same time the US experienced a post-9/11 slowdown.

By the way, the US is generally the great Satan in AGW circles because its per capita CO2 production is the highest in the world. But this is in part because our economic output per capita is close to the highest in the world. The US is about in the middle of the pack in efficiency, though behind many European countries which have much higher fuel taxes and heavier nuclear investments.

As an interesting side note, the US per capita CO2 emissions, as show below, have actually been flat to down since the early 1970’s. To the extent that Europe is doing better at CO2 reduction than the US, it may actually be more of an artifact of their declining populations vs. America’s continued growth.

Finally, if you get really tired of the US-bashing, you can take some comfort that though the US is the #1 per capita producer of CO2, of which we are uncertain is even harmful, we have done a fabulous job reducing many other pollutants we are much more certain are harmful. For example, the US has much lower SO2 production than most European nations and the water quality is better. One could argue that the US has spent its abatement dollars on things that really matter.

Cost of the Solutions vs. the Benefits: Why Warmer but Richer may be Better than Colder and Poorer

If you get beyond the hard core of near religious believers in the massive warming scenarios, the average global warming supporter would answer this paper by saying: "Yes there is a lot of uncertainty, but though the doomsday warming scenarios via runaway positive feedback in the climate can’t be proven, they are so bad that we need to cut back on CO2 production just to be on the safe side."

This would be a perfectly reasonable approach if cutting back on CO2 production was nearly cost-free. But it is not. The burning of hydrocarbons that create CO2 is an entrenched part of our lives and our economies. Forty years ago we might have had an easier time of it, as we were on a path to dramatically cut back on CO2 production via what is still the only viable technology to massively replace fossil fuel consumption — nuclear power. Ironically, it was environmentalists that shut down this effort, and power industries around the world replaced capacity that would have gone nuclear mostly with coal, the worst fossil fuel in terms of CO2 production (per BTU of power, Nuclear and hydrogen produce no CO2, natural gas produces some, gasoline produces more, and coal produces the most).

Just halting CO2 production at current levels (not even rolling it back) would knock several points off of world economic growth. Every point of economic growth you knock off guarantees you that you will get more poverty, more disease, more early death. If you could, politically, even make such a freeze stick, you would lock China and India, nearly 2 billion people, into continued poverty just when they were about to escape it. You would in the process make the world less secure, because growing wealth is always the best way to maintain peace. Right now, China can become wealthier from peaceful internal growth than it can from trying to loot its neighbors. But in a zero sum world created by a CO2 freeze, countries like China would have much more incentive to create trouble outside its borders. This tradeoff is often referred to as a cooler but poorer world vs. a richer but warmer world. Its not at all clear which is better.

What impact, warming?

We’ve already discussed just how much the popular media has overblown the effect of warming. Sea levels may rise, but only by 15 inches in one hundred years, and even that based on arguably over-inflated IPCC models. There is no evidence that weather patterns will be more severe, or that diseases will spread, or that species will be threatened by warming. And, since most of the warming has been and will be concentrated in winter and nights, we will see rising temperatures more in a narrowing of temperature variability rather than a drastic increase in summer high temperatures. Growing seasons, in turn, will be longer and deaths from cold, which tend to outnumber heat-related deaths, will decline.

What impact, Intervention?

While the Kyoto treaty was a massively-flawed document, with current technologies a Kyoto type cap and trade approach is about the only way we have available to slow or halt CO2 emissions. And, unlike the impact of warming on the world, the impact of such a intervention is very well understood by the world’s economists and seldom in fact disputed by global warming advocates. Capping world CO2 production would by definition cap world economic growth at the rate of energy efficiency growth, a number at least two points below projected real economic growth. In addition, investment would shift from microprocessors and consumer products and new drug research and even other types of pollution control to energy. The effects of two points or more lower economic growth over 50-100 years can be devastating:

Remember the power of compounded growth rates we discussed earlier. A world real economic growth rate of 4% yields income fifty times higher in a hundred years. A world real economic growth rate two points lower yields income only 7 times higher in 100 years. So a two point reduction in growth rates reduces incomes in 100 years by a factor of seven! This is enormous. It means, literally, that on average everyone in a cooler world would make 1/7 what they would make in a warmer world.

Currently, there are perhaps a billion people, mostly in Asia, poised to exit millennia of subsistence poverty and reach the middle class. Global warming intervention will likely consign these folks to continued poverty. Does anyone remember that old ethics problem, the one about having a button that every time you pushed it, you got a thousand dollars but someone in China died. Global warming intervention strikes me as a similar issue – intellectuals in the west feel better about man being in harmony with the Earth but a billion Asians get locked into poverty.

Lower world economic growth will in turn considerably shorten the lives of billions of the world’s poor

A poorer world is more vulnerable to natural disasters. While AGW advocates worry (needlessly) about hurricanes and tornados in a warmer world, what we can be certain of is that these storms will be more devastating and kill more people in a poorer world than a richer one.

The unprecedented progress the world is experiencing in slowing birth rates, due entirely to rising wealth, will likely be reversed. A cooler world will not only be poorer, but likely more populous as well. It will also be a hungrier world, particularly if a cooler world does indeed result in lower food production than a warmer world

A transformation to a prosperous middle class in Asia will make the world a much safer and more stable place, particularly vs. a cooler world with a billion Asian poor people who know that their march to progress was halted by western meddling.

A cooler world would ironically likely be an environmentally messier world. While anti-growth folks blame all environmental messes on progress, the fact is that environmental impact is a sort of inverted parabola when plotted against growth. Early industrial growth tends to pollute things up, but further growth and wealth provides the resources and technology to clean things up. The US was a cleaner place in 1970 than in 1900, and a cleaner place today than in 1970. Stopping or drastically slowing worldwide growth would lock much of the developing world, countries like Brazil and China and Indonesia, into the top end of the parabola. Is Brazil, for example, more likely to burn up its rain forest if it is poor or rich?

If global warming is real and its effects will one day be as devastating as some believe is likely, then greater economic growth would, by increasing greenhouse gas (GHG) emissions, sooner or later lead to greater damages from climate change. On the other hand, by increasing wealth, technological development and human capital, economic growth would broadly increase human well-being, and society’s capacity to reduce climate change damages via adaptation or mitigation. Hence, the conundrum: at what point in the future would the benefits of a richer and more technologically advanced world be canceled out by the costs of a warmer world?

Indur Goklany attempted to shed light on this conundrum in a recent paper presented at the 25th Annual North American Conference of the US Association for Energy Economics, in Denver (Sept. 21, 2005). His paper — "Is a richer-but-warmer world better than poorer-but-cooler worlds?” — which can be found here, draws upon the results of a series of UK Government-sponsored studies which employed the IPCC’s emissions scenarios to project future climate change between 1990 and 2100 and its global impacts on various climate-sensitive determinants of human and environmental well-being (such as malaria, hunger, water shortage, coastal flooding, and habitat loss). The results indicate that notwithstanding climate change, through much of this century, human well-being is likely to be highest in the richest-but-warmest world and lower in poorer-but-cooler worlds. With respect to environmental well-being, matters may be best under the former world for some critical environmental indicators through 2085-2100, but not necessarily for others.

This conclusion casts doubt on a key premise implicit in all calls to take actions now that would go beyond “no-regret” policies in order to reduce GHG emissions in the near term, namely, a richer-but-warmer world will, before too long, necessarily be worse for the globe than a poorer-but-cooler world. But the above analysis suggests this is unlikely to happen, at least until after the 2085-2100 period.

Policy Alternatives

Above, we looked at the effect of a cap and trade scheme, which would have about the same effect as some type of carbon tax. This is the best possible approach, if an interventionist approach is taken. Any other is worse.

The primary other alternative bandied about by scientists is some type of alternative energy Manhattan project. This can only be a disaster. Many scientists are technocratic fascists at heart, and are convinced that if only they could run the economy or some part of it, instead of relying on this messy bottom-up spontaneous order we call the marketplace, things, well, would be better. The problem is that scientists, no matter how smart they are, miss with their bets because the economy, and thus the lowest cost approach to less CO2 production, is too complicated for anyone to understand or manage. And even if the scientists stumbled on the right approaches, the political process would just screw the solution up. Probably the number one alternative energy program in the US is ethanol subsidies, which are scientifically insane since ethanol actually increases rather than reduces fossil fuel consumption. Political subsidies almost always lead to investments tailored just to capture the subsidy, that do little to solve the underlying problem. In Arizona, we have thousands of cars with subsidized conversions to engines that burn multiple fuels but never burn anything but gasoline. In California, there are hundreds of massive windmills that never turn, having already served their purpose to capture a subsidy. In California, the state bent over backwards to encourage electric cars, but in fact a different technology, the hybrid, has taken off.

Besides, when has this government led technology revolution approach ever worked? I would say twice – once for the Atomic bomb and the second time to get to the moon. And what did either get us? The first got us something I am not sure we even should want, with very little carryover into the civilian world. The second got us a big scientific dead end, and probably set back our space efforts by getting us to the moon 30 years or so before we were really ready to do something about it or follow up the efforts.

If we must intervene to limit CO2, we should jack up the price of fossil fuels with taxes, or institute a cap and trade scheme which will result in about the same price increase, and the market through millions of individual efforts will find the lowest cost net way to reach whatever energy consumption level you want with the least possible cost. (The only real current alternative that is rapidly deploy-able to reduce CO2 emissions anyway is nuclear power, which could be a solution but was killed by…the very people now wailing about global warming.)

As stated in the introduction, the purpose of this paper has not been to provide a balanced portrayal of Anthropogenic Global Warming (AGW) theory; its purpose instead is to provide a comprehensive overview of skeptic’s concerns with AGW theory. However, the issues raised here are not necessarily new, and AGW supporters have attempted to address many of them.

The New Scientist, a fairly strong and reliable voice for advocacy of anthropogenic global warming theory, recently published its response to what it calls 26 myths about global warming, many of these “myths” being correlated loosely with skeptics concerns about AGW theory as outlined in this paper. Walking through their points seems a reasonable way to entertain a rebuttal to the skeptic’s position. Each of these has a link to the New Scientist article in question. I have tried to summarize the position with a quote, shown in italics. My response to each then follows.

Before I get into these 20 myths, note that many of the key skeptic’s questions are neatly avoided. While the magazine gives itself certain softball questions, it does not attempt to take on skeptics questions such as:

Isn’t warming from CO2 a diminishing return, such that each 10ppm of CO2 has less warming effect than the last 10 ppm?

Isn’t warming from CO2 asymptotic, such that total warming from CO2 is capped?

Isn’t 2/3 or more of the future warming in IPCC forecasts due to positive feedback effects that tend to be rare in stable systems and that even the IPCC admits are poorly understood?

Aren’t there a lot of problems with ground-based temperature measurements?

Aren’t the historical proxies for temperature diverging from measurements, such that the IPCC actually dropped many of the recent proxy measurements to hide this result?

There are many others, but we can get at them tangentially through dealing with the 20 “myths” below

So what’s going on? It is true that human emissions of CO2 are small compared with natural sources. But the fact that CO2 levels have remained steady until very recently shows that natural emissions are usually balanced by natural absorptions. Now slightly more CO2 must be entering the atmosphere than is being soaked up by carbon "sinks".

Though I do know that some skeptics will claim that man can’t be changing world CO2 levels, I don’t believe I even tried to make that claim in this paper.

The more salient point in asking whether human CO2 emissions are too tiny to matter is to ask whether the change in composition of the atmosphere of 0.009% by human activities is substantial enough to affect world climate in any important way, particularly when the portion being increased, CO2, is a relatively weak greenhouse gas vs. other portions.

It is true that the action taken so far, such as the Kyoto Protocol, will only have a marginal effect. The protocol’s authors have always described it as a first step. But even before it came into effect in 2005, the protocol has triggered some profound thinking among governments, corporations and citizens about their carbon footprint and how to reduce it. Industrialized countries such as the UK are planning for emissions reductions of 60% or more by mid-century.

This is a bit of a straw man. Certainly to the extent that man is causing climate change, men with enough will can do something about it. The question is whether the costs justify the avoided change – this is a question that I have addressed sufficiently and won’t revisit here. However, I would like to comment on this:

We may find that once the process has begun, the world loses its addiction to carbon fuels surprisingly quickly. Natural scientists fear “tipping points” in the climate system. But there are also tipping points in social, economic and political systems. Once under way, things can happen fast…

This is a statement to which I both agree and disagree. I am a technological optimist, and so generally accept that world-changing technologies will continue to spring from man’s mind, and that the introduction of these changes can be fast and their impact dramatic. The only reason that I am a tad skeptical about this statement is that the vast majority of strong AGW adherents are technology pessimists, so it would be uncharacteristic for them to take such a position. Absent unimagined new technologies, change of the type AGW supporters are hoping for is actually not a positive feedback process as implied in this statement. Why is it that climate scientists see so many positive feedback processes, when these are actually so rare? In fact, most investment decisions, for example investments to reduce CO2 emissions, follow a diminishing return relationship. Early investors capture the low-hanging fruit, while each successive wave of investment offers a lower return (here, in CO2 reduction) for each incremental dollar invested.

Most researchers would agree that while the original hockey stick can – and has – been improved in a number of ways, it was not far off the mark. Most later temperature reconstructions fall within the error bars of the original hockey stick. Some show far more variability leading up to the 20th century than the hockey stick, but none suggest that it has been warmer at any time in the past 1000 years than in the last part of the 20th century.

No one statement by AGW supporters would do more to build my confidence in their findings than to actually have someone say “the Mann hockey stick was a deeply flawed analysis, and we have taken great pains to make sure the flaws identified in Mann are not present in other historical reconstructions.” However, when I see the statement above, I am left to wonder if any of the flaws in Mann have actually been corrected in other works, or if systematic errors still exist. Since AGW supporters refuse to acknowledge flaws in Mann, it is almost certain that these flaws still exist in the other analyses (therefore making it unsurprising that new analyses show roughly the same results). Remember that Mann was replaced by Biffra as lead author of this section of the Fourth IPCC report, and it was Biffra who dropped 20-30 years of recent data from his historical reconstruction when it did not show the result that he wanted it to.

Getting reasonably accurate predictions is a matter of choosing the right timescale: days in the case of weather, decades in the case of climate.

Climate scientists sometimes refer to the effects of chaos as intrinsic or unforced variability: the unpredictable changes that arise from the dynamic interactions between the oceans and atmosphere rather than being a result of "forcings" such as changes in solar irradiance or greenhouse gases.

The crucial point is that unforced variability occurs within a relatively narrow range. It is constrained by the major factors influencing climate: it might make some winters bit a warmer, for instance, but it cannot make winters warmer than summers

There are systems people who would both agree and disagree with this statement. The real study of chaotic systems is barely older than the study of global warming, and most mathematicians would say that the issue of long-term predictability of macro trends in chaotic systems is not settled science.

However, one issue the statement overlooks is that even if chaotic systems have some long-term order, at least when “viewed from a distance,” this does not mean that the drivers of those long-term trends can be discerned by those of us standing in the chaos. So while it may be theoretically possible to predict long-scale climate changes, it may still be impossible to discern the true drivers of these climate systems amidst the chaos, making the long-term prediction problem moot.

Remember, no one has a thermometer that provides two readings – temperature due to “natural” causes and temperature due to man-made forcings. The only argument one can make outside of a laboratory is to try to correlate temperature changes to certain other variables, like CO2 level. But in a chaotic system, when thousands of variables may matter, and there are all kinds of cross-dependencies between variables, definitively showing direct correlation, much less causation, is very hard, possibly impossible. Remember, outside lab experiments, climate scientists main argument that CO2 is causing current warming is “We have checked everything else it possibly could be, and it wasn’t those things, so it must be CO2.” In a chaotic system, such a statement borders on hubris.

Climate is average weather, and it can vary unpredictably only within the limits set by major influences like the Sun and levels of greenhouse gases in the atmosphere. We might not be able to say whether it will rain at noon in a week’s time, but we can be confident that the summers will be hotter than winters for as long as the Earth’s axis remains tilted.

The validity of models can be tested against climate history. If they can predict the past (which the best models are pretty good at) they are probably on the right track for predicting the future – and indeed have successfully done so.

I hope that if you have learned anything from this paper, you already know how to refute the statement above. Climate models match history because they have been tuned and tweaked and overridden to do so. The fact that they then can reproduce history is meaningless. Even more, you should run away quickly from anyone who makes this statement, because they are either ignorant of what they are talking about or they are trying to sell you the Brooklyn Bridge.

Finally, the claim is sometimes made that if computer models were any good, people would be using them to predict the stock market. Well, they are!

A lot of trading in the financial markets is already carried out by computers. Many base their decisions on fairly simple algorithms designed to exploit tiny profit margins, but others rely on more sophisticated long-term models.

Sorry, but this is a facile and ignorant mis-interpretation of what financial models are doing. Yes, people are running long-term financial models as part of a trading strategy, but these models feed into very short-term trading decisions. If you looked at the output from these long-term models, you would see that they are changing constantly as new data flows in. There is an old joke about two campers who see a bear growling at them. One of them starts putting his tennis shoes on. The other one says to him “Why are you putting your shoes on? You can’t outrun that bear.” His friend replied “I don’t have to outrun the bear. I just have to outrun you.” Traders’ long-term models work the same. They don’t actually expect them to be right, they just want them to be better, based on current conditions, than other traders’ models, then they can make money.

Indeed they did…. However, Schneider soon realised he had overestimated the cooling effect of aerosol pollution and underestimated the effect of CO2, meaning warming was more likely than cooling in the long run….

The calls for action to prevent further human-induced global warming, by contrast, are based on an enormous body of research by thousands of scientists over more than a century that has been subjected to intense – and sometimes ferocious – scrutiny. According to the latest IPCC report, it is more than 90% certain that the world is already warming as a result of human activity

We have already dealt with aerosols, and unlike many skeptics I have not really held the 1970’s global cooling panic against the climate community. The last paragraph is just circular. Saying the IPCC is 90% sure does not answer the arguments about what skeptics feel the IPCC is ignoring.

First of all, it is worth bearing in mind that any data on global temperatures before about 150 years ago is an estimate, a reconstruction based on second-hand evidence such as ice cores and isotopic ratios. The evidence becomes sparser the further back we look, and its interpretation often involves a set of assumptions. In other words, a fair amount of guesswork.

This is hilarious. What happened to their confidence in Mann and 1000-year temperature reconstructions just a few myths back? But to continue, the answer is basically yes, but:

The important question is what is causing the current, rapid warming? We cannot dismiss it as natural variation just because the planet has been warmer at various times in the past. Many studies suggest it can only be explained by taking into account human activity.

Nor does the fact that it has been warmer in the past mean that future warming is nothing to worry about. The sea level has been tens of metres higher during past warm periods, enough to submerge most major cities around the world.

Here is why it matters – beyond the laboratory evidence of the greenhouse effect, which tells us merely that there is an affect and not how strong it is, the main evidence cited by AGW supporters for current warming being man-made is to try to show that current warming is somehow unprecedented, and therefore unlikely to be natural. So it is odd here that AGW supporters simply shrug their shoulders here and say that it is not important that current warming be unprecedented.

This does not sound too bad, and for many people it won’t be. Wealthy individuals and countries will be able to adapt to most short-term changes, whether it means buying an air conditioner or switching to crops better suited to the changing climate. Rainfall will fall in mid-latitudes but rise in high latitudes, and initially agricultural yields will probably. Some regions will suffer, though. Africa could be hardest hit, with yields predicted to halve in some countries as early as 2020.

As global temperature climbs to 3°C above present levels – which is likely to happen before the end of this century if greenhouse emissions continue unabated – the consequences will become increasingly severe. More than a third of species face extinction. Agricultural yields will start to fall in many parts of the world. Millions of people will be at risk from coastal flooding. Heatwaves, droughts, floods and wildfires will take an ever greater toll.

I hope readers will accept that I am not exaggerating or constructing straw men when I talk about the dire predictions by AGW supporters. There is nothing here that we have not dealt with earlier, except perhaps the rainfall. Of late, AGW supporters seem to have shifted to rainfall (rather than sea level rise) as their lead scary topic. Note, however, that even the IPCC admits that it and all of its modelers really do not understand (even a little bit) the effect of global warming on rainfall and drought. Logic says that with more water evaporated, while global warming may cause now local draughts, overall rainfall should increase. I would bet any amount of money that lower economic growth due to aggressive CO2 abatement will have a far more deleterious effect on worldwide agricultural yields than global warming.

So what role, if any, have solar fluctuations had in recent temperature changes? While we can work out how Earth’s orbit has changed going back many millions of years, we have no first-hand record of the changes in solar output associated with sunspots before the 20th century.

It is true that sunspot records go back to the 17th century, but sunspots actually block the Sun’s radiation. It is the smaller bright spots (faculae) that increase the Sun’s output and these were not recorded until more recently. The correlation between sunspots and bright faculae is not perfect, so estimates of solar activity based on sunspot records may be out by as much as 30%.

The other method of working out past solar activity is to measure levels of carbon-14 and beryllium-10 in tree rings and ice cores. These isotopes are formed when cosmic rays hit the atmosphere, and higher sunspot activity is associated with increases in the solar wind that deflect more galactic cosmic rays away from Earth. Yet again, though, the correlation is not perfect. What is more, recent evidence suggests that the deposition of beryllium-10 can be affected by climate changes, making it even less reliable as a measure of past solar activity.

This is again a pretty hilarious statement. One could easily argue that temperature and CO2 proxies have at least as much uncertainty. One wonders why AGW advocates do not seem as concerned about the errors in the proxies they hold dear. But anyway, to continue:

But even if solar forcing in the past was more important than this estimate suggests, as some scientists think, there is no correlation between solar activity and the strong warming during the past 40 years. Claims that this is the case have not stood up to scrutiny (pdf document).

Similarly, there is no trend in direct measurements of the Sun’s ultraviolet output and in cosmic rays. So for the period for which we have direct, reliable records, the Earth has warmed dramatically even though there has been no corresponding rise in any kind of solar activity.

This is another you-study-my-study pissing match. I am happy to admit that our knowledge of the sun’s changing impact on climate is poor, and that it is hard to separate out this one effect in a chaotic system. I refuse to fall into the same scientific hubris as AGW supporters. However, those who think the sun has some contribution to warming are buttressed by the knowledge that they are working with the main driver of climate, rather than a secondary variable.

There is no convincing evidence that cosmic rays are a major factor determining cloud cover. The ionising of air by cosmic rays will impart an electric charge to aerosols, which in theory could encourage them to clump together to form particles large enough for cloud droplets to form around, called "cloud condensation nuclei".

But cloud physicists say it has yet to be shown that such clumping occurs. And even if it does, it seems far-fetched to expect any great effect on the amount of clouds in the atmosphere. Most of the atmosphere, even relatively clean marine air, has plenty of cloud condensation nuclei already.

A series of attempts by Svensmark to show an effect have come unstuck. Initially, Svensmark claimed there was a correlation between cosmic ray intensity and satellite measurements of total cloud cover since the 1980s – yet a correlation does not prove cause and effect. It could equally well reflect changes in solar irradiance, which inversely correlate with cosmic ray intensity.

I am starting to notice a trend here of making statements about competing that could be applied equally well to AGW theory. And what about all those points they made above, reminding us over and over that CO2 greenhouse theory works in the lab. Now the lab is not good enough?

However, I would accept that the cosmic ray theory is pretty undeveloped and not acceptably proven. It has had a number of fits and starts. Just like CO2 greenhouse theory, the cosmic ray effect on climate can be reproduced in the lab, but it is really hard to parse out its effects in the chaotic climate.

At some of these overlaps, the atmosphere already absorbs 100% of radiation, meaning that adding more greenhouse gases cannot increase absorption at these specific frequencies. For other frequencies, only a small proportion is currently absorbed, so higher levels of greenhouse gases do make a difference.

This means that when it comes to the greenhouse effect, two plus two does not equal four.

Wow! An AGW supporter actually said this in public. This is to our point that there is a diminishing return from incremental CO2 in the atmosphere. Of course, they say this in the context of trying to show why water isn’t as important as it might seem, but still, it’s there

But the overall quantities of these other gases are tiny. Even allowing for the relative strength of the effects, CO2 is still responsible for two-thirds of the additional warming caused by all the greenhouse gases emitted as a result of human activity.

Water vapour will play a huge role in the centuries to come, though. Climate models, backed by satellite measurements, suggest that the amount of water vapour in the upper troposphere (about 5 to 10 kilometres up) will double by the end of this century as temperatures rise.

This will result in roughly twice as much warming than if water vapour remained constant. Changes in clouds could lead to even greater amplification of the warming or reduce it – there is great uncertainty about this. What is certain is that, in the jargon of climate science, water vapour is a feedback, but not a forcing.

Again, I am not getting into this, we covered it plenty in the paper. When they say “CO2 is still responsible for two-thirds of the additional warming” (and remember this is an output of their models, not any other analysis) what they really mean is that “our models that were programmed to have CO2 drive the climate show that CO2 drives the climate.” Note that in a three paragraph answer about the effect of water vapor as a climate feedback, only three words – “or reduce it” – acknowledge that it might actually have a negative feedback effect, despite the fact that even the IPCC includes cloud cover as a negative feedback. They just don’t want to admit a negative feedback might even exist.

One study in Science revealed errors in the way satellite data had been collected and interpreted. For instance, the orbit of satellites gradually slows, which has to be taken into account because it affects the time of day at which temperature recording are taken. This problem was always recognised, but the corrections were given the wrong sign (negative instead positive and vice versa).

A second study, also in Science, looked at the weather balloon data. Measurements of the air temperature during the day can be skewed if the instruments are heated by sunlight. Over the years the makers of weather balloons had come up with better methods of preventing or correcting for this effect, but because no one had taken these improvements into account, the more accurate measurements appeared to show daytime temperatures getting cooler.

The corrected temperature records show that tropospheric temperatures are indeed rising at roughly the same rate as surface temperatures. Or, as a 2006 report by the US Climate Change Science Program (pdf) puts it: "For recent decades, all current atmospheric data sets now show global-average warming that is similar to the surface warming." This one appears settled.

There is still some ambiguity in the tropics, where most measurements show the surface warming faster than the upper troposphere, whereas the models predict faster warming of the atmosphere. However, this is a minor discrepancy compared with cooling of the entire troposphere and could just be due to the errors of margin inherent in both the observations and the models.

First, observe absolutely ruthless efforts to apply corrections and adjustments to any measurement that does not fit their theory, while blithely accepting the surface temperature measurements that we showed can be really unreliable. Given the choice of focusing on managing satellite temperatures up or surface temperature down, you can see which they chose. Second, note that this is another narrow one study conclusion. AGW supporters frequently cite single studies (conducted by AGW supporters) that overturn skeptics arguments as having “settled” the issue. There are still many reasons to think that troposphere temperature increases are less than surface increases. Finally, even temperature increases that were the same between the surface and the troposphere would be a real problem for AGW theory. The authors here act like this surface-troposphere issue is a minor deal, but in fact if AGW theory is right, the troposphere has to warm more, because that is where the extra heat is being absorbed. This is not at all settled.

It is clear that the Antarctic Peninsula, which juts out from the mainland of Antarctica towards South America, has warmed significantly. The continent’s interior was thought to have warmed too, but in 2002 a new analysis of records from 1966 to 2000 concluded that it has cooled overall….

Climate models do not predict an evenly spread warming of the whole planet: changes in wind patterns and ocean currents can change the distribution of heat, leading to some parts warming much faster than average, while others cool at first.

Now the authors of the 2006 study have submitted a correction (pdf format). It turns out that a fault in the software on some of the floats led to some temperature measurements being associated with the wrong depth.

Meanwhile, work by other teams suggests that the past warmth of the oceans has been overestimated. The problem was due to expendable sensors that are thrown overboard and take measurements as they sink.

I never had heard the claim that the oceans were cooling, so it does not surprise me that they are not. However, it is again interesting the amount of due diligence that AGW supporter put in to the correction of any temperature measurement the might refute global warming, while blithely accepting the atrocious condition and biases in ground-based temperature measurement because, well, because these instruments are telling the story they want to hear.

The mid-century cooling appears to have been largely due to a high concentration of sulphate aerosols in the atmosphere, emitted by industrial activities and volcanic eruptions. Sulphate aerosols have a cooling effect on the climate because they scatter light from the Sun, reflecting its energy back out into space.

The rise in sulphate aerosols was largely due to the increase in industrial activities at the end of the second world war. In addition, the large eruption of Mount Agung in 1963 produced aerosols which cooled the lower atmosphere by about 0.5°C, while solar activity levelled off after increasing at the beginning of the century

I think I was pretty fair in discussing the aerosol cooling hypothesis in this paper, though many would disagree with the above statement’s certainty.

Climate models that take into account only natural factors, such as solar activity and volcanic eruptions, do not reproduce 20th century temperatures very well. If, however, the models include human emissions, including greenhouse gases and aerosols, they accurately reproduce the 1940 to 1970 dip in temperatures.

I hope readers who have made it this far can supply the refutation of this point: Wrong, wrong, wrong. Climate models initially matched history poorly. Today they match well because they have been tweaked and adjusted and forced to match. They match because they are programmed to match. And, as we discussed, they match only because they make ridiculously low assumptions for natural forcings, and assume all natural forcings causing temperatures to rise in the first half of the century magically reversed in 1950, though there is no good evidence for it.

In the southern hemisphere, the picture is even more mixed, with evidence of both warm and cool periods around this time. The Medieval Warm Period may have been partly a regional phenomenon, with the extremes reflecting a redistribution of heat around the planet rather than a big overall rise in the average global temperature.

What is clear, both from the temperature reconstructions and from independent evidence – such as the extent of the recent melting of mountain glaciers – is that the planet has been warmer in the past few decades than at any time during the medieval period. In fact, the world may not have been so warm for 6000 or even 125,000 years (see Climate myths: It has been warmer in the past, what’s the big deal?).

What really matters, though, is not how warm it is now, but how warm it is going to get in the future. Even the temperature reconstructions that show the greatest variations in the past 1000 years suggest up until the 1980s, average temperature changes remained within a narrow band spanning 1ºC at most. Now we are climbing out of that band, and the latest IPCC report (pdf format) predicts a further rise of 0.5ºC by 2030 and a whopping 6.4ºC by 2100 in the worst case scenario.

We have covered this pretty well in this paper, so again I won’t go back into it, except to highlight a couple of things we can learn from this statement. First, note the hubris again – it is warmer today than in the last 125,000 years. I sure wish there was a way to bet on this – I would have only a one in 125,000 chance of being wrong in betting against this statement. Second, note the use of the worst case scenarios. For 2100, we don’t get the best case or even the average case, we get the worst case. Can you name another branch of science where people do this? Can you imagine, say, a group out to measure the speed of light. They are going to get some middle figure with an error band of some range. Wouldn’t you expect them to day that they found the speed of light to be so-and-so, plus or minus an error of such-and-such size? If they were climate scientists, they would instead announce that they have found the speed of light could be as large as Z, that being the highest possible figure in their error band.

Yet while there is some evidence of cold intervals in parts of the southern hemisphere during this time, they do not appear to coincide with those in the northern hemisphere. Such findings suggest the Little Ice Age may have been more of a regional phenomenon than a global one.

Solar radiation was probably lower at times during this period, especially during a dip in solar activity called the Maunder minimum around 1700, but models and temperature reconstructions suggest this would have reduced average global temperatures by 0.4ºC at most.

The larger falls in temperature in Europe and North American may have been due to changes in atmospheric circulation over the North Atlantic, or in the Gulf Stream, or both, reducing heat transport from the tropics (see Climate change sceptics lose vital argument).

The warming after the so-called Little Ice Age may reflect both an increase in solar activity and a redistribution of heat around the planet. In particular, the increase in global temperature in the first half of the 20th century may have been largely due to an increase in solar activity. The continued warming in recent decades, however, cannot be explained by increases in solar radiation alone

Remember the graphs we showed earlier – the arctic proxies look like the current warming is a straight linear increase from the 1700s to today. In fact, in the IPCC spaghetti graph showing all those historic reconstructions, they all show a natural warming from the 18th and 19th century through the 20th. Again, AGW supporters really need to explain why they are so confident that this natural warming trend stopped in 1945 or so, exactly and coincidently at the exact same moment that man-made forcings caused the world to continue to warm, coincidently at about the same rate it was warming naturally earlier in the century.

Few scientists think there will be a rapid shutdown of circulation. Most ocean models predict no more than a slowdown, probably towards the end of the century. This could slow or even reverse some of the warming due to human emissions of greenhouse gases, which might even be welcome in an overheated Europe, but the continent is not likely to get colder than it is at present.

A slowdown in circulation would affect many parts of the world by disrupting global rainfall patterns. But these effects will be insignificant compared with the much greater changes global warming will cause

It takes about 5000 years for an ice age to end and, after the initial 800 year lag, temperature and CO2 concentrations in the atmosphere rise together for a further 4200 years.

What seems to have happened at the end of the recent ice ages is that some factor – most probably orbital changes – caused a rise in temperature. This led to an increase in CO2, resulting in further warming that caused more CO2 to be released and so on: a positive feedback that amplified a small change in temperature. At some point, the shrinking of the ice sheets further amplified the warming.

Models suggest that rising greenhouse gases, including CO2, explains about 40% of the warming as the ice ages ended. The figure is uncertain because it depends on how the extent of ice coverage changed over time, and there is no way to pin this down precisely.

I was extremely happy to see that they at least tried to address the issue I raised, ie is it really realistic to have a process dominated by positive feedback, and if so, why doesn’t it run away. Their answer:

Finally, if higher temperatures lead to more CO2 and more CO2 leads to higher temperatures, why doesn’t this positive feedback lead to a runaway greenhouse effect? There are various limiting factors that kick in, the most important being that infrared radiation emitted by Earth increases exponentially with temperature, so as long as some infrared can escape from the atmosphere, at some point heat loss catches up with heat retention.

Which might make sense EXCEPT that they are claiming that today’s temperature and level of CO2 are higher than these historical levels, so we are already higher than the level where they claim “heat loss catches up with heat retention.” So either their answer is right, and there is a strong compensating process which is not built into their models, or they are wrong and they still need to explain what keeps a positive feedback dominated process from running away.

The question is whether this is real or just a reflection of the problems with working out the age of the trapped air and with deuterium as a temperature indicator. Many researchers are working on ways to independently date the air and the ice, and to improve temperature reconstructions based on relative deuterium content. One involves working out what is called the deuterium excess by comparing the relative amounts of deuterium and oxygen-18 in the ice.

The deuterium excess reflects the temperature at the sea surface where the water that later fell as snow evaporated, rather than the surface temperature where the snow fell. It helps to reveal whether variations in the relative deuterium content of the ice are a result of water coming from a different source region rather than changes in local temperature.

In 2001, researchers used the deuterium excess to correct for some of the problems with the temperature record of the Vostok ice core. Their results produce a much closer fit between temperature and CO2 levels and reduces the mismatch around 120,000 years ago to a few thousand years.

I did not really raise this issue, as even the most enthusiastic AGW supporter does not tend to claim that CO2 drives all historic temperature changes. However, again, note the pattern – any historic data that does not fit with AGW data typically is scrutinized and “corrected.” Articles discussing flaws in methodology in gathering such data are quickly published. Contrast this with the difficulty scientists have in questioning any data that supports AGW theory. As we saw earlier, the New Scientist still can’t bring itself to utter the words “the Mann hockey stick was flawed.” Neither could the IPCC, they just sort of dropped it, or buried it in the midst of 12 others, without even saying why the analysis that was the centerpiece of their last report was strangely missing.

The Sun’s energy output has not increased since direct measurements began in 1978. If increased solar output really was responsible, we should be seeing warming on all the planets and their moons, not just Mars and Pluto.

Our solar system has eight planets, three dwarf planets and quite a few moons with at least a rudimentary atmosphere, and thus a climate of sorts. Their climates will be affected by local factors such as orbital variations, changes in reflectance (albedo) and even volcanic eruptions, so it would not be surprising if several planets and moons turn out to be warming at any one time.

I agree we have a lot to learn about this, and nothing at all is settled. However, we now have evidence from at least 5 other terrestrial bodies that are warming at the same time the Earth is warming. Why do AGW supporters resist at least investigating further?

This appears to be the biggest recent list of sceptics. Yet many, if not most, of the 60 signatories are not actively engaged in studying climate change: some are not scientists at all and at least 15 are retired.

Compare that with the dozens of statements on climate change from various scientific organisations around the world representing tens of thousands of scientists, the consensus position represented by the IPCC reports and the 11,000 signatories to a petition condemning the Bush administration’s stance on climate science.

I have carefully avoided the game of dueling scientific numbers. As to the claim that the skeptic list “are not actively engaged in studying climate change: some are not scientists at all and at least 15 are retired” I would be thrilled if AGW supporters held to this standard in making their own numbers. But, they manage to abandon this standard by the next paragraph, when they claim the pro-AGW numbers, like the 11,000, are open to the same criticism (since there are only 500-600 true climate scientists in the world, vs. physicist, meteorologists, etc).

Now that there is a consensus, those whose findings challenge the orthodoxy are always going have a tougher time convincing their peers, as in any field of science. For this reason, there will inevitably be pressure on scientists who challenge the consensus. But findings or ideas that clash with the idea of human-induced global warming have not been suppressed or ignored – far from it.

Journalists do have an interest in promoting themselves (and their books), while their employers want to boost their audience and sell advertising. Publicity helps with all these aims, but you get far more publicity by challenging the mainstream view than by promoting it. Which helps explain why so many sections of the media continue to publish or broadcast the claims of deniers, regardless of their merit.

The notion of a “conspiracy” of course, is a useful straw man, implying devious villains in the SPECTRE conference room planning the overthrow of the world. I won’t argue the point again, except to encourage you to watch the news with a critical eye, and decide for yourself. However, just to get you started, ask yourself if these events are signs of healthy, unbiased science:

·A group of AGW supporters are trying to get the British government to use force to block the publication of a skeptical movie (the Global Warming Swindle)

·AGW supporters in California have included skeptical scientists such as MIT’s Dr. Richard Lindzen as defendants in a law suit, asking that damages be paid by people and companies whose public speech doesn’t conform to AGW theory

·Many AGW skeptics have been unable to get scientists who have published publicly funded research to reveal their data and methodology for critique. Freedom of Information Act (FOIA) requests have become a necessary tool of climate skeptics.

·When a group began photographing temperature measurement points to document the shortcomings in historical surface temperature measurements, the NOAA pulled the locations of its measurement stations off the Internet so that these US citizens could no longer take pictures of and critique US government installations.

·Scientists who question AGW theory are equated by AGW supporters with Holocaust deniers.

Yet another complicating factor is that changes in climate can also change the paths that tropical cyclones tend to take, determining whether they remain over oceans or strike land.

What every one agrees on is that over the past few decades there has been a huge rise in the number of people being killed or injured by hurricanes, and in damage to infrastructure, and this trend looks set to continue. The main reason for this, however, is that more and more people are living and building in hurricane zones.

Most of these three paragraphs is entirely correct – there is no evidence that hurricane numbers or intensity are effected by global warming, and if they are, whether they are increased or decreased. However, Hurricane Katrina was most certainly NOT caused by global warming. Why can’t they just say that? It may have been made stronger or weaker. Its course may have been altered. But it was not created by warming. By the way, the year after Katrina saw a much smaller than average Atlantic hurricane season.

But it is extremely difficult to generalise about the overall impact on plant growth. Numerous groups around the world have been conducting experiments in which plots of land are supplied with enhanced CO2, while comparable nearby plots remain at normal levels.

While these experiments typically have found initial elevations in the rate of plant growth, these have tended to level off within a few years. In most cases this has been found to be the result of some other limiting factor, such as the availability of nitrogen or water.

So the answer is yes, but there is a diminishing return at some point. Isn’t that the same as can be said for the CO2 greenhouse effect?

Predicting the world’s overall changes in food production in response to elevated CO2 is virtually impossible. Global production is expected to rise until the increase in local average temperatures exceeds 3°C, but then start to fall. In tropical and dry regions increases of just 1 to 2°C are expected to lead to falls in production. In marginal lands where water is the greatest constraint, which includes much of the developing world but also regions such as the western US, the losses may greatly exceed the gains.

Have you noticed yet that things that might hurt the AGW-interventionist’s case always seem “impossible to predict” while the climate is well within our prediction capabilities?

As for food crops, the factors are more complex. The crops most widely used in the world for food in many cases depend on particular combinations of soil type, climate, moisture, weather patterns and the infrastructure of equipment, experience and distribution systems. If the climate warms so much that crops no longer thrive in their traditional settings, farming of some crops may be able to shift to adjacent areas, but others may not. Rich farmers and countries will be able to adapt more easily than poorer ones.

I love the rich-poor language. The leftish New Scientist simply can’t help itself. But I will accept this statement, and go further: This is the reason that aggressive actions to reduce CO2 that reduce economic growth, particularly in the developing world, may not make sense. To the extent that some climate change will occur no matter what, or is already programmed by our past actions, then a richer world can deal with it better than a poorer one.

Yet recently there have been claims that polar bear populations are increasing. So what’s going on? There are thought to be between 20,000 and 25,000 polar bears in 19 population groups around the Arctic. While polar bear numbers are increasing in two of these populations, two others are definitely in decline. We don’t really know how the rest of the populations are faring, so the truth is that no one can say for sure how overall numbers are changing.

Again, I love this. We can know the global temperature increase over a century to a tenth of a degree but it is impossible to count polar bears.

Note that down 30% (which coming from an environmental advocacy ground has got to be considered the most extreme possible estimate) is not “extinct.” The article fails to address at all the issue that polar bears have survived through eras when Arctic sea ice melted completely in the summers. And there are many reasons for threats to polar bear numbers – most experts would say that hunting and threats to habitat are much more important factors than global temperatures.

There is a burgeoning grass roots movement (described here, in part) to better document key temperature measurement stations both to better correct past measurements as well as to better understand the quality of the measurements we are getting.Steve McIntyre has had some back and forth conversations with Eli Rabbett about temperature measurement points, each accusing the other of cherry-picking their examples of bad and good installations. McIntyre therefore digs into one of the example temperature measurement points Rabbett offers as a cherry-picked example of a good measurement point. For this cherry-picked good example of a historical temperature measurement point, here are the adjustments that are made to this site’s measurements before it is crunched up into the official historic global warming numbers:

Corrections have been made for:– relocation combined with a transition of large open hut to a wooden Stevenson screen (September 1950) [ed: This correction was about 1°C]– relocation of the Stevenson screen (August 1951).– lowering of Stevenson screen from 2.2 m to 1.5 m (June 1961).– transition of artificial ventilated Stevenson screen to the current KNMI round-plated screen (June 1993).– warming trend of 0.11°C per century caused by urban warming.

Note that these corrections, which are by their nature guesstimates, add up to well over 1 degree C, and therefore are larger in magnitude than the global warming that scientists are trying to measure. In other words, the noise is larger than the signal.Postscript: 0.11C per century is arguably way too low an estimate for urban warming.

It turns out to be quite easy to do a simple but fairly robust reality check of global warming forecasts, even without knowing what a "Watt" or a "forcing" is. Our approach will be entirely empirical, based on the last 100 years of climate history. I am sensitive that we skeptics not fall into the 9/11 Truther syndrome of arguing against a coherent theory from isolated anomalies. To this end, my approach here is holistic and not anomaly driven. What we will find is that, extrapolating from history, it is almost impossible to get warming numbers as high as those quoted by global warming alarmists.

Climate Sensitivity

The one simple concept you need to understand is "climate sensitivity." As used in most global warming literature, climate sensitivity is the amount of global warming that results from a doubling in atmospheric CO2 concentrations. Usually, when this number is presented, it refers to the warming from a doubling of CO2 concentrations since the beginning of the industrial revolution. The pre-industrial concentration is generally accepted as 280ppm (0.028% of the atmosphere) and the number today is about 380ppm, so a doubling would be to 560ppm.

As a useful, though not required, first step before we begin, I encourage you to read the RealClimate simple "proof" for laymen that the climate sensitivity is 3ÂºC, meaning the world will warm 3 degrees C with a doubling of CO2 concentrations from their pre-industrial level. Don’t worry if you don’t understand the whole description, we are going to do it a different, and I think more compelling, way (climate scientists are a bit like the Wizard of Oz — they are afraid if they make things too simple someone might doubt they are a real wizard). 3ÂºC is a common number for sensitivity used by global warming hawks, though it is actually at the low end of the range that the UN IPCC arrived at in their fourth report. The IPCC (4th report, page 798) said that the expected value is between 3ÂºC and 4ÂºC and that there was a greater chance the sensitivity was larger than 6ÂºC than that it was 1.5ÂºC or less. I will show you why I think it is extraordinarily unlikely that the number is greater even than 1.5ÂºC.

Our Approach

We are going to derive the sensitivity (actually a reasonable range for sensitivity) for ourselves in three steps. First, we will do it a simple way. Then, we will do it a slightly harder but more accurate way. And third, we will see what we would have to assume to get a number anywhere near 3ÂºC. Our approach will be entirely empirical, using past changes in CO2 and temperature to estimate sensitivity. After all, we have measured CO2 going up by about 100 ppm. That is about 36% of the way towards a doubling from 280 to 560. And, we have measured temperatures — and though there are a lot of biases in these temperature measurements, these measurements certainly are better than our guesses, say, of temperatures in the last ice age. Did you notice something odd, by the way, in the RealClimate derivation? They never mentioned measured sensitivities in the last 100 years — they jumped all the way back to the last ice age. I wonder if there is a reason for that?

A First Approximation

OK, let’s do the obvious. If we have experienced 36% of a doubling, then we should be able to take the historic temperature rise from CO2 for the same period and multiply it by 2.8 (that’s just reciprocal of 36%) and derive the temperature increase we would expect for a full doubling.

The problem is that we don’t know the historic temperature rise solely form CO2. But we do know how to bound it. The IPCC and most global warming hawks place the warming since 1900 at about 0.6ÂºC. Since no one attributes warming before 1900 to man-made CO2 (it did warm, but this is attributed to natural cyclical recovery from the little ice age) then the maximum historic man-made warming is 0.6ÂºC. In fact, all of that warming is probably not from CO2. Some probably is from continued cyclical warming out of the little ice age. Some, I believe strongly, is due to still uncorrected biases, particularly of urban heat islands, in surface temperature data.

But let’s for a moment attribute, unrealistically, all of this 0.6ÂºC to man-made CO2 (this is in fact what the IPCC does in their report). This should place an upper bound on the sensitivity number. Taking 0.6ÂºC times 2.8 yields an estimated climate sensitivity of 1.7ÂºC. Oops. This is about half of the RealClimate number or the IPCC number! And if we take a more realistic number for man-made historic warming as 0.4ÂºC, then we get a sensitivity of 1.1ÂºC. Wow, that’s a lot lower! We must be missing something important! It turns out that we are, in this simple analysis, missing something important. But taking it into account is going to push our sensitivity number even lower.

A Better Approximation

What we are missing is that the relation between CO2 concentration and warming is not linear, as implied in our first approximation. It is a diminishing return. This means that the first 50 ppm rise in CO2 concentrations causes more warming than the next 50 ppm, etc. This effect has often been compared to painting a window. The first coat of paint blocks out a lot of light, but the window is still translucent. The next coat blocks out more light, but not as much as the first. Eventually, subsequent coats have no effect because all the light is already blocked. CO2 has a similar effect on warming. It only absorbs certain wavelengths of radiation returning to space from earth. Once the absorption of those wavelengths is saturated, extra CO2 will do almost nothing. (update: By the way, this is not some skeptic’s fantasy — everyone in climate accepts this fact).

So what does this mean in English? Well, in our first approximation, we assumed that 36% of a CO2 doubling would yield 36% of the temperature we would get in a doubling. But in reality, since the relationship is a diminishing return, the first 36% of a CO2 doubling will yield MORE than 36% of the temperature increase you get for a doubling. The temperature increase is front-loaded, and diminishes going forward. An illustration is below, with the linear extrapolation in red and the more realistic decreasing exponential extrapolation in blue.

The exact shape and equation of this curve is not really known, but we can establish a reasonable range of potential values. For any reasonable shapes of this curve, 36% of a CO2 doubling (where we are today) equates to from 43% to 63% of the final temperature increase over a doubling. This would imply that a multiplier between 2.3 and 1.6 for temperature extrapolation (vs. 2.8 derived above for the straight linear extrapolation above) or a climate sensitivity of 1.4ÂºC to 1.0ÂºC if man-made historic warming was 0.6ÂºC and a range of 0.9ÂºC to 0.6ÂºC for a man-made historic warming of 0.4ÂºC. I tend to use the middle of this range, with a multiplier of about 1.9 and a man-made historic warming of 0.5ÂºC to give a expected sensitivity of 0.95ÂºC, which we can round to 1ÂºC.

This is why you will often hear skeptics cite numbers closer to 1ÂºC rather than 3ÂºC for the climate sensitivity. Any reasonable analysis of actual climate experience over the last 100 years yields a sensitivity much closer to 1ÂºC than 3ÂºC. Most studies conducted before the current infatuation with showing cataclysmic warming forecasts came up with this same 1ÂºC, and peer-reviewed work is still coming up with this same number.

So what does this mean for the future? Well, to predict actual temperature increases from this sensitivity, we would have to first create a CO2 production forecast and, you guessed it, global warming hawks have exaggerated that as well. The IPCC says we will hit the full doubling to 560ppm around 2065 (Al Gore, incredibly, says we will hit it in the next two decades). This means that with about 0.5C behind us, and a 3 sensitivity, we can expect 2.5C more warming in the next 60 years. Multiply that times exaggerated negative effects of warming, and you get instant crisis.

However, since actual CO2 production is already below IPCC forecasts, we might take a more reasonable date of 2080-2100 for a doubling to 560. And, combining this with our derived sensitivity of 1ÂºC (rather than RealClimate’s 3ÂºC) we will get 0.5C more warming in the next 75-100 years. This is about the magnitude of warming we experienced in the last century, and most of us did not even notice.

I know you are scratching you head and wondering what trick I pulled to get numbers so much less than the scientific "consensus." But there is no trick, all my numbers are empirical and right out of the IPCC reports. In fact, due to measurement biases and other climate effects that drive warming, I actually think the historic warming from CO2 and thus the sensitivity is even lower, but I didn’t want to confuse the message.

So what are climate change hawks assuming that I have not included? Well, it turns out they add on two things, neither of which has much empirical evidence behind it. It is in fact the climate hawks, not the skeptics, that need to argue for a couple of anomalies to try to make their case.

Is Climate Dominated by Positive Feedback?

Many climate scientists argue that there are positive feedbacks in the climate system that tend to magnify and amplify the warming from CO2. For example, a positive feedback might be that hotter climate melts sea ice and glaciers, which reduces the reflectiveness of the earth’s surface, which causes more sunlight to be absorbed, which warms things further. A negative feedback might be that warmer climate vaporizes more water which forms more clouds which blocks sunlight and cools the earth.

Climate scientists who are strong proponents of catastrophic man-made warming theory assume that the climate is dominated by positive feedbacks. In fact, my reading of the IPCC report says that the climate "consensus" is that net feedback in the climate system is positive and tends to add 2 more degrees of temperature for every one added from CO2. You might be thinking – aha – I see how they got a sensitivity of 3ÂºC: Your 1ÂºC plus 2ÂºC in feedback equals 3ÂºC.

But there is a problem with that. In fact, there are three problems with this. Here they are:

We came up with our 1ÂºC sensitivity empirically. In other words, we observed a 100ppm past CO2 increase leading to 0.5ÂºC measured temperature increase which implies 1ÂºC sensitivity. But since this is empirical, rather than developed from some set of forcings and computer models, then it should already be net of all feedbacks. If there are positive feedbacks in the system, then they have been operating and should be part of that 1ÂºC.

There is no good scientific evidence that there is a large net positive feedback loop in climate, or even that the feedback is net positive at all. There are various studies, hypotheses, models, etc., but no proof at all. In fact, you can guess this from our empirical data. History implies that there can’t be any large positive feedbacks in the system or else we would have observed higher temperatures historically. In fact, we can go back in to the distant historical record (in fact, Al Gore showed the chart I am thinking of in An Inconvenient Truth) and find that temperatures have never run away or exhibited any sort of tipping point effect.

The notion that a system like climate, which has been reasonably stable for millions of years, is dominated by positive feedback should offend the intuition of any scientist. Nature is dominated in large part by negative feedback processes. Positive feedback processes are highly unstable, and tend to run away to a distant endpoint. Nuclear fission, for example, is a positive feedback process

Do aerosols and dimming imply a higher sensitivity?

Finally, the last argument that climate hawks would employ is that anthropogenic effects, specifically emission of SO2 aerosols and carbon black, have been reflecting sunlight and offsetting the global warming effect. But, they caution, once we eliminate these pollutants, which we have done in the West (only to be offset in China and Asia) temperatures will no longer be suppressed and we will see the full extent of warming.

First, again, no one really has any clue the magnitude of this effect, or even if it is an effect at all. Second, its reach will tend to be localized over industrial areas (since their presence in the atmosphere is relatively short-lived), whereas CO2 acts worldwide. If these aerosols and carbon black are concentrated say over 20% of the land surface of the world, this means they are only affecting the temperature over 5% of the total earth’ s surface. So its hard to argue they are that significant.

However, let’s say for a moment this effect does exist. How large would it have to be to argue that a 3.0ÂºC climate sensitivity is justified by historical data? Well, taking 3.0ÂºC and dividing by our derived extrapolation multiplier of 1.9, we get required historic warming due to man’s efforts of 1.6ÂºC. This means that even if all past 0.6ÂºC of warming is due to man (a stretch), then aerosols must be suppressing a full 1ÂºC of warming. I can’t say this is impossible, but it is highly unlikely and certainly absolutely no empirical evidence exists to support any number like this. Particularly since dimming effects probably are localized, you would need as much as 20ÂºC suppression in these local areas to get a 1ÂºC global effect. Not very likely.

Why the number might even be less

Remember that when we calculated sensitivity, we needed the historical warming due to man’s CO2. A simple equation for arriving at this number is:

This is why most skeptics care if surface temperature measurements are biased upwards or if the sun is increasing in intensity. Global warming advocates scoff and say that these effects don’t undermine greenhouse gas theory. And they don’t. I accept greenhouse gases cause some warming. BUT, the more surface temperature measurements are biased upwards and the more warming is being driven by non-anthropogenic sources, the less that is being caused by man. And, as you have seen in this post, the less warming caused by man historically means less that we will see in the future. And while global warming hawks want to paint skeptics as "deniers", we skeptics want to argue the much more interesting question "Yes, but how much is the world warming, and does this amount of warming really justify the costs of abatement, which are enormous."